1. Field of the Invention
This invention relates to an optical fibre sensor assembly. More particularly, this invention relates to optical fibre sensor assemblies used to sense changes in temperature, strain, pressure, magnetic fields, electric fields, displacement and acceleration.
2. Discussion of the Prior Art
Many such assemblies, comprising arrays of sensor elements, have been made. They are optically addressed using a variety of well-known multiplexing techniques and combinations thereof, see for example U.S. Pat. No. 5,365,359. In such assemblies, the number of sensors that can be multiplexed is limited for a variety of reasons. For example, in a time-division multiplexed array, only about 60 sensors can be multiplexed onto a single launch/return fibre pair. This can be increased by using a combination of time-division multiplexing (TDM) and wavelength-division multiplexing (WDM). This technique has been limited by the requirement to use signals that are relatively well-spaced in the wavelength regime. This restriction of wavelength spacing limits the number of sensors that can be addressed (see A. R. Davis et al, 12th Int. Conf. On Optical Fibre Sensors Proceedings, Opt. Soc. America 1997, p. 616-619). U.S. Pat. No. 5,696,857 describes a system using a combination of frequency-division multiplexing (FDM) and wavelength-division multiplexing.